Expression of Heparin/Heparan Sulfate Interacting Protein/Ribosomal Protein L29 During the Estrous Cycle and Early Pregnancy in the Mouse1

Using a variety of approaches, we have examined the expression of the heparin/heparan sulfate (Hp/HS) interacting protein/ribosomal protein L29 (HIP/RPL29) in mouse uteri during the estrous cycle and early pregnancy. HIP/RPL29 selectively binds heparin and HS and may promote HS-dependent embryo adhesion. HIP/RPL29 was prominently expressed in both luminal and glandular epithelia under almost all conditions, including the phase of embryo attachment. In contrast, differences were noted in HIP/RPL29 expression in the stromal compartment both during the estrous cycle and during early pregnancy. Most notably, HIP/RPL29 accumulated in decidua, where it displayed a pattern complementary to that of pericellular deposition of the HS proteoglycan, perlecan. HIP/RPL29 protein was detected in implanted embryos at both initial and later stages of implantation; however, embryonic HIP/RPL29 mRNA accumulation was more pronounced at later stages (Day 7.5 postcoitum). In situ hybridization revealed similar spatial changes for HIP/RPL29 mRNA during these different physiological states. Whereas differences in the spatial pattern of HIP/RPL29 protein and mRNA expression were demonstrable, little change was detected in the level of HIP/RPL29 mRNA or protein in total endometrial extracts. Mouse blastocysts attached, but did not outgrow, on surfaces coated with recombinant murine HIP/RPL29. Surprisingly, soluble glycosaminoglycans including heparin, low molecular weight heparin, or chondroitin sulfate were not able to inhibit embryo attachment to HIP/RPL29-coated surfaces. These latter observations indicate that embryonic cell surface components other than HS proteoglycans can promote binding to HIP/RPL29 expressed by uterine cells.